Several things to try
- satin pillowcase or satin sleeping cap plus 'pineapple' or braid at night
- switch from commercial shampoo to conditioner only washing
- use a leave in conditioner renowned for 'slip', there are several curly kids haircare ranges that will likely have decent products (Curly Q's, Ouidad Krly Kids, Blended Cutie, Mixed Chicks Kids, Kinky Curly Tiny Twirls)
- don't comb damp because you will damage her hair, either dripping wet and drenched in conditioner or dry starting from the bottom and working up (many curlies do not comb daily)
- may want to wash three times a week in order to detangle: this will be much less like hell if you follow all the above!

Detangling with fingers is gentlest, followed by a double row detangling comb. Some curlies like the Tangle Teezer brush. Those with thicker hair generally need to detangle in small sections.Tangle Teezer the Detangling Hair Care Brand